1 Digital Imaging and Communications in Medicine (DICOM) Part 10: Media Storage and File Format for Media Interchange Published by National Electrical Manufacturers Association 1300 N. 17th Street Rosslyn, Virginia USA Copyright 2011 by the National Electrical Manufacturers Association. All rights including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literacy and Artistic Works, and the International and Pan American Copyright Conventions.
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3 Page 3 CONTENTS NOTICE AND DISCLAIMER. 2 CONTENTS.. 3 FOREWORD. 5 1 Scope and Field of Application 6 2 References NORMATIVE REFERENCES. 7 3 Definitions REFERENCE MODEL DEFINITIONS SERVICE CONVENTIONS DEFINITIONS PRESENTATION SERVICE DEFINITIONS DICOM INTRODUCTION AND OVERVIEW DEFINITIONS DICOM INFORMATION OBJECT DEFINITIONS DICOM DATA STRUCTURE AND ENCODING DEFINITIONS DICOM MESSAGE EXCHANGE DEFINITIONS DICOM MEDIA STORAGE AND FILE FORMAT DEFINITIONS Symbols and Abbreviations 11 5 Conventions 11 6 DICOM Models for Media Storage GENERAL DICOM COMMUNICATION MODEL THE DICOM MEDIA STORAGE MODEL Physical Media Layer Media Format Layer DICOM Data Format Layer DICOM SOP Classes Concept of the DICOM File Format DICOM Medical Information Directory DICOM Media Storage Application Profiles Media Storage and the DICOM Standard Structure DICOM File Format DICOM FILE META INFORMATION DATA SET ENCAPSULATION SUPPORT OF FILE MANAGEMENT INFORMATION SECURE DICOM FILE FORMAT DICOM File Service FILE-SET FILE IDS FILE MANAGEMENT ROLES AND SERVICES FILE CONTENT ACCESS CHARACTER SET RESERVED DICOMDIR FILE ID 26
4 Page 4 9 Conformance Requirements.. 27 Annex A Example of DICOMDIR File Content (Informative).. 29 A.1 SIMPLE DIRECTORY CONTENT EXAMPLE. 29 A.2 EXAMPLE OF DICOMDIR FILE CONTENT WITH MULTIPLE REFERENCED FILES. 32 Annex B HL7 Structured Document Files. 33 Annex C Index of Attribute Tags and UIDs (Informative).. 35
5 Page 5 FOREWORD This DICOM Standard was developed according to procedures of the DICOM Standards Committee. The DICOM Standard is structured as a multi-part document using the guidelines established in the following document: ISO/IEC Directives, 1989 part 3 - Drafting and Presentation of International Standards. PS 3.1 should be used as the base reference for the current parts of this Standard.
6 Page 6 1 Scope and Field of Application This Part of the DICOM Standard specifies a general model for the storage of Medical Imaging information on removable media. The purpose of this Part is to provide a framework allowing the interchange of various types of medical images and related information on a broad range of physical storage media. This Part specifies: a. a layered model for the storage of medical images and related information on storage media. This model introduces the concept of Media Storage Application Profiles, which specify application specific subsets of the DICOM Standard to which a Media Storage implementation may claim conformance. Such a conformance applies only to the writing, reading and updating of the content of storage media. Specific Application Profiles are not included in this Part but in PS 3.11 of the DICOM Standard; b. a DICOM File Format supporting the encapsulation of any Information Object Definition; c. a Secure DICOM File Format supporting the encapsulation of a DICOM File Format in a cryptographic envelope; d. a DICOM File Service providing independence from the underlying media format and physical media. The policies specific to the DICOMDIR file used to store the Media Storage Directory Service/Object Pair Class are also addressed. This Part is related to other parts of the DICOM Standard in that: - PS 3.2, Conformance, specifies the requirements that shall be met to achieve DICOM Conformance in Media Storage; - PS 3.3, Information Object Definitions, specifies a number of Information Object Definitions (e.g., various types of images) which may be used in conjunction with this part; - PS 3.4, builds upon this part to define the Media Storage Service Class; - PS 3.5, Data Structure and Encoding, addresses the encoding rules necessary to construct a Data Set which is encapsulated in a file as specified in this part; - PS 3.6, Data Dictionary, contains a registry by Tag of all Data Elements related to the Attributes of Information Objects defined in PS 3.3. This index includes the Value Representation and Value Multiplicity for each Data Element; - PS 3.11, Media Storage Application Profiles standardizes a number of choices related to a specific clinical need (selection of a Physical Medium and Media Format as well as specific Service/Object Pair Classes). It aims at facilitating the interoperability between implementations that claim conformance to the same Application Profile. PS 3.11 is intended to be extended as the clinical needs for Media Storage Interchange evolve; - PS 3.12, Media Formats and Physical Media for Data Interchange, defines a number of selected Physical Medium and corresponding Media Formats. These Media Formats and Physical Medium selections are referenced by one or more of the Application Profiles of PS PS 3.12 is intended to be extended as the technologies related to Physical Medium evolve. - PS 3.15, Security Profiles defines a number of profiles for use with Secure DICOM Media Storage Application Profiles. The Media Storage Security Profiles specify the cryptographic techniques to be used for each Secure DICOM File in a Secure Media Storage Application Profile.
7 Page 7 PS 3.10 lays a foundation for open Media Interchange by standardizing an overall architecture and addressing some of the major barriers to interoperability: the definition of a DICOM File Format, a DICOM File Service and the policies associated with a Media Storage Directory structure. Note: PS 3.3 specifies a general medical imaging Basic Directory Information Object Definition and PS 3.4 specifies the corresponding Media Storage Directory SOP Class that is a member of the Media Storage Service Class. Adherence to the provisions of DICOM PS 3.10 by implementations reading, writing or updating Storage Media represents a key foundation for open Storage Media Interchange. However, it is only with the selection of standard Physical Media and corresponding Media Formats in PS 3.12 and the use of specific Application Profiles in PS 3.11 that effective Media Storage Interchange interoperability is achieved. Therefore, claiming conformance to DICOM PS 3.10 only, is not a valid DICOM Conformance Statement. DICOM Media Storage Conformance shall be made in relation to a PS 3.11 Application Profile according to the framework defined by PS References 2.1 NORMATIVE REFERENCES The following standards contain provisions that, through reference in this text, constitute provisions of this Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Standard are encouraged to investigate the possibilities of applying the most recent editions of the standards indicated below. ISO/IEC Directives, 1989 Part 3 - Drafting and presentation of International Standards. ISO , Information Processing Systems - Open Systems Interconnection - Basic Reference Model. ISO , Information processing systems - Open Systems Interconnection - Basic reference Model - Part 2: Security Architecture ISO/TR 8509, Information Processing Systems - Open Systems Interconnection - Service Conventions ISO 8822, Information Processing Systems - Open Systems Interconnection - Connection-Oriented Presentation Service Definition. ISO 8859, Information Processing - 8-bit single-byte coded graphic character sets - Part 1: Latin Alphabet No. 1 NEMA PS Digital Imaging and Communications in Medicine - Part 1, Introduction and Overview of Part 1 through 9. NEMA PS Digital Imaging and Communications in Medicine - Part 2, Conformance. NEMA PS Digital Imaging and Communications in Medicine - Part 3, Information Object Definitions NEMA PS Digital Imaging and Communications in Medicine - Part 4, Service Class Specifications NEMA PS Digital Imaging and Communications in Medicine - Part 5, Data Structures and Encoding NEMA PS Digital Imaging and Communications in Medicine - Part 6, Data Dictionary NEMA PS Digital Imaging and Communications in Medicine - Part 7, Message Exchange NEMA PS Digital Imaging and Communications in Medicine - Part 8, Network Communication Support for Message Exchange
8 Page 8 NEMA PS Digital Imaging and Communications in Medicine - Part 11, Media Storage Application Profiles. NEMA PS Digital Imaging and Communications in Medicine - Part 12, Media Formats and Physical Media for Data Interchange. RFC-3369, Cryptographic Message Syntax, August 2002 RFC 2557 MIME Encapsulation of Aggregate Documents, such as HTML (MHTML) 3 Definitions For the purposes of this Standard the following definitions apply. 3.1 REFERENCE MODEL DEFINITIONS This Part of the Standard is based on the concepts developed in ISO and makes use of the following terms defined in it: a. Application Entity; b. Application Process; c. Service or Layer Service; d. Transfer Syntax. This Part of the Standard makes use of the following terms defined in ISO : a. Data Confidentiality Note: The definition is the property that information is not made available or disclosed to unauthorized individuals, entities or processes. b. Data Origin Authentication Note: The definition is the corroboration that the source of data received is as claimed. c. Data Integrity Note: The definition is the property that data has not been altered or destroyed in an unauthorized manner. 3.2 SERVICE CONVENTIONS DEFINITIONS This Part of the Standard makes use of the following terms defined in ISO/TR 8509: a. Service Provider; b. Service User.
9 Page PRESENTATION SERVICE DEFINITIONS This Part of the Standard makes use of the following terms defined in ISO 8822: a. Abstract Syntax; b. Abstract Syntax Name. 3.4 DICOM INTRODUCTION AND OVERVIEW DEFINITIONS This Part of the Standard makes use of the following terms defined in PS 3.1 of the DICOM Standard: - Attribute. 3.5 DICOM INFORMATION OBJECT DEFINITIONS This Part of the Standard makes use of the following terms defined in PS 3.3 of the DICOM Standard: a. Information Object Definition. 3.6 DICOM DATA STRUCTURE AND ENCODING DEFINITIONS This Part of the Standard makes use of the following terms defined in PS 3.5 of the DICOM Standard: a. Data Element; b. Data Set; c. Data Element Type; d. Value; e. Value Multiplicity; f. Value Representation; 3.7 DICOM MESSAGE EXCHANGE DEFINITIONS This Part of the Standard makes use of the following terms defined in PS 3.7 of the DICOM Standard: a. Service Object Pair (SOP) Class; b. Service Object Pair (SOP) Instance; c. Implementation Class UID. 3.8 DICOM MEDIA STORAGE AND FILE FORMAT DEFINITIONS The following definitions are commonly used in this Part of the Standard: Application Profile: A Media Storage Application Profile defines a selection of choices at the various layers of the DICOM Media Storage Model that are applicable to a specific need or context in which the media interchange is intended to be performed. DICOM File Service: The DICOM File Service specifies a minimum abstract view of files to be provided by the Media Format Layer. Constraining access to the content of files by the Application Entities through such a DICOM File Service boundary ensures Media Format and Physical Media independence. DICOM File: A DICOM File is a File with a content formatted according to the requirements of this Part of the DICOM Standard. In particular such files shall contain, the File Meta Information and a properly formatted Data Set.
10 Page 10 DICOMDIR File: A unique and mandatory DICOM File within a File-set that contains the Media Storage Directory SOP Class. This File is given a single component File ID, DICOMDIR. File: A File is an ordered string of zero or more bytes, where the first byte is at the beginning of the file and the last byte at the end of the File. Files are identified by a unique File ID and may by written, read and/or deleted. File ID: Files are identified by a File ID that is unique within the context of the File-set they belong to. A set of ordered File ID Components (up to a maximum of eight) forms a File ID. File ID Component: A string of one to eight characters of a defined character set. File Meta Information: The File Meta Information includes identifying information on the encapsulated Data Set. It is a mandatory header at the beginning of every DICOM File. File-set: A File-set is a collection of DICOM Files (and possibly non-dicom Files) that share a common naming space within which File IDs are unique. File-set Creator: An Application Entity that creates the DICOMDIR File (see section 8.6) and zero or more DICOM Files. File-set Reader: An Application Entity that accesses one or more files in a File-set. File-set Updater: An Application Entity that accesses Files, creates additional Files, or deletes existing Files in a File-set. A File-set Updater makes the appropriate alterations to the DICOMDIR file reflecting the additions or deletions. DICOM File Format: The DICOM File Format provides a means to encapsulate in a File the Data Set representing a SOP Instance related to a DICOM Information Object. Media Format: Data structures and associated policies that organize the bit streams defined by the Physical Media format into data file structures and associated file directories. Media Storage Model: The DICOM Media Storage Model pertains to the data structures used at different layers to achieve interoperability through media interchange. Media Storage Services: DICOM Media Storage Services define a set of operations with media that facilitate storage to and retrieval from the media of DICOM SOP Instances. Physical Media: A piece of material with recording capabilities for streams of bits. Characteristics of a Physical Media include form factor, mechanical characteristics, recording properties and rules for recording and organizing bit streams in accessible structures Secure DICOM File: A DICOM File that is encapsulated with the Cryptographic Message Syntax specified in RFC Secure File-set: A File-set in which all DICOM Files are Secure DICOM Files. Secure Media Storage Application Profile: A DICOM Media Storage Application Profile that requires a Secure File-set.
11 Page 11 4 Symbols and Abbreviations The following symbols and abbreviations are used in this Part of the Standard. ACC ACR ASCII AE ANSI CEN/TC/251 American College of Cardiology American College of Radiology American Standard Code for Information Interchange Application Entity American National Standards Institute Comite Europeen de Normalisation - Technical Committee Medical Informatics DICOM Digital Imaging and Communications in Medicine FSC File-set Creator FSR File-set Reader FSU File-set Updater HL7 Health Level 7 HTML Hypertext Transfer Markup Language IEEE Institute of Electrical and Electronics Engineers ISO International Standards Organization ID Identifier IOD Information Object Definition JIRA Japan Industries Association of Radiological Systems MIME Multipurpose Internet Mail Extensions NEMA National Electrical Manufacturers Association OSI Open Systems Interconnection SOP Service-Object Pair TCP/IP Transmission Control Protocol/Internet Protocol UID Unique Identifier VR Value Representation XML Extensible Markup Language 5 Conventions Words are capitalized in this document to help the reader understand that these words have been previously defined in Section 3 of this document and are to be interpreted with that meaning. A Tag is represented as (gggg,eeee), where gggg equates to the Group Number and eeee equates to the Element Number within that Group. Tags are represented in hexadecimal notation as specified in PS 3.5 of the DICOM Standard.. Attributes of File Meta Information are assigned a Type which indicates if a specific Attribute is required depending on the Media Storage Services. The following Type designations are derived from the PS 3.5 designations but take into account the Media Storage environment:
12 Page 12 - Type 1: Such Attributes shall be present with an explicit Value in files created by File-set Creators and File-set Updaters. They shall be supported by File-set Readers and File-set Updaters; - Type 1C: Such Attributes shall be present with an explicit Value in Files created by File-set Creators and File-set Updaters if the specified condition is met. They shall be supported by File-set Readers and File-set Updaters. - Type 2: Such Attributes shall be present with an explicit Value or with a zero-length Value if unknown, in Files created by File-set Creators and File-set Updaters. They shall be supported by File-set Readers and File-set Updaters; - Type 2C: Such Attributes shall be present with an explicit Value or with a zero-length if unknown, in Files created by File-set Creators and File-set Updaters if the specified condition is met. They shall be supported by File-set Readers and File-set Updaters; - Type 3: Such Attributes may be present with an explicit Value or a zero-length Value in Files created by File-set Creators and File-set Updaters. They may be supported or ignored by File-set Readers and File-set Updaters. 6 DICOM Models for Media Storage This section defines the DICOM Media Storage Model used by DICOM Application Entities for the purpose of communication through the interchange of removable storage media. Specifically, this Section provides a model to clarify a number of concepts for digital imaging and communications and introduces key terms used throughout the DICOM Standard. This model has been used to partition the DICOM Standard into separate parts related to storage media interchange. 6.1 GENERAL DICOM COMMUNICATION MODEL Figure presents the general communication model of DICOM which spans network and storage media interchange communications. The DICOM Application Entities may rely on either one of the following boundaries: a. the OSI Upper Layer Service, which provides independence from specific physical networking communication support b. the DICOM File Service, which provides access to Storage Media independently from specific physical media storage formats and file structures.
13 Page 13 Medical Imaging Application DICOM Application Message Exchange Upper Layer Service Boundar y DICOM Upper Layer Protocol for TCP/IP Medium A Medium B Medium C File Service Boundary TCP/IP Media Format & Physical Medium Media Format & Physical Medium Media Format & Physical Medium Network Storage Media Interchange 6.2 THE DICOM MEDIA STORAGE MODEL Figure General DICOM Communication Model The DICOM Media Storage Model is presented by Figure and expands on the General DICOM Communication Model introduced earlier in Section 6.1. The DICOM Media Storage Model focuses on the aspects directly related to data interchange through removable storage media. It pertains to the data structures and associated rules used at different layers to achieve interoperability through media interchange. The Services identified in this Model are simple boundaries between functional layers. Note: It is not within the scope of this Standard to specify Application Programming Interfaces at these boundaries.
14 Page 14 Application Entity Basic Directory Service/Object Pairs DICOM File Format Media Formats e.g. Data Structures of a File System, which may be physical media specific Physical Media Storage media specifications e.g. CD-R, 90mm MOD, 130mm MOD, etc. Application Services boundary relies on DICOM Info. Objects and Media Storage Service Classes DICOM Data Format Layer DICOM File Services boundary ensures media format & physical media independance Media Format Layer Physical Media Access Services boundary physical media specific Physical Media Format Layer Application Specific Information Objects (Images, Results, etc..) Generic Elements addressed in this Part (independent of specific Physical Media & Information Objects) Abstract Services providing access to the data structures of the underlying layer Figure DICOM Media Storage Model The DICOM Media Storage Model includes three layers, which are described in the following sections Physical Media Layer Physical media characteristics are defined at the Physical Media Layer. Such characteristics include the physical media form factor, dimension, mechanical characteristics and recording properties. This Layer also defines the organization and grouping of the recorded bits. Notes: 1. An example of a Physical Media Layer in the personal computer environment is the 3 1/2 inch floppy disk, double sided, high density. 2. The specification of one or more specific Physical Media for a given application is beyond the scope of this Part of the DICOM Standard. PS 3.12 of the DICOM Standard and its annexes specify several Physical Media choices. PS 3.11 defines a number of Application Profiles which select specific Physical Media depending on the requirements of specific medical imaging applications.
15 Page Media Format Layer At the Media Format Layer, Physical Media bit streams are organized into specific structures. Data file structures and associated directory structures are defined to allow efficient access and management of the physical media space. Note: This layer is often specific to a given operating system environment. An example of such a Media Format Layer definition associated with the 3 1/2 inch floppy disk are the data structures used by the operating systems of various personal computer file systems. PS 3.12 of the DICOM Standard and its annexes specify several Media Format choices. Media Formats supported by the DICOM Standard are selected to support the minimum requirements specified by the DICOM File Service as specified in Section 8 of this Part. Constraining access to the File content through such a DICOM File Service ensures that the DICOM Data Format Layer is independent from Media Format and Physical Media selection DICOM Data Format Layer The DICOM Data Format Layer includes four elements of specification: a. DICOM Media Storage SOP Classes and associated Information Object Definitions; b. The DICOM File Format; c. The Secure DICOM File Format; d. The DICOM Media Storage Directory SOP Class; e. DICOM Media Storage Application Profiles; f. DICOM Security Profiles for Media Storage DICOM SOP Classes DICOM SOP Classes and associated Information Object Definitions (IODs) are used to convey specific medical imaging information at the Data Format Layer. SOP Classes and IODs used for Media Storage shall follow the framework established in PS 3.3 and PS 3.4 of the DICOM Standard. Examples of such IODs are modality images, patient information, results, etc. The use of DICOM IODs in conjunction with Media Storage Services forms a number of Media Storage Service Object Pair Classes or SOP Classes. Media Storage Services (e.g., read, write, delete, etc.) shall be performed through the DICOM File Service. The content of the resulting DICOM Files shall be formatted according to the DICOM File Format as specified below. Notes: 1. The concept of a SOP Class in the Media Storage context is equivalent to the concept of SOP Class introduced in PS 3.3 and PS 3.4 for network related operations (DIMSE Operations). 2. Both Composite and Normalized IODs and SOP Classes may be used in the Media Storage context. PS 3.4 of the DICOM Standard defines a number of SOP Classes that may be used for Media Storage. These SOP Classes are based on DICOM Standard IODs that may be found in the Annexes to DICOM PS 3.3. The structure and encoding of a Data Set representing the data associated with a SOP Class shall follow PS 3.5 of the DICOM Standard. The specification of Transfer Syntaxes that may be used to encode such a Data Set, is also defined in PS Concept of the DICOM File Format The encapsulation of a DICOM Data Set in a File shall follow the specifications of Section 7 of this Part. These encapsulation rules define a DICOM File Format able to contain in a File any DICOM Data set.
16 Page 16 Files are identified by File IDs. No semantics shall be inferred from these File IDs, nor from their structure. Note: A medical imaging application acting as a creator of a DICOM File may use semantic information to generate a File ID, but readers of DICOM files should not rely on apparent semantic content of a File ID. Data Set encapsulation shall be based on the DICOM File Service as specified in Section 8 of this Part. Note: It is acceptable that a specific Media Format offers more file services than those specified in the DICOM File Service. Such services may be local or internal to an implementation. Their usage is beyond the scope of the DICOM Standard. However, in cases where such services are reflected in the file structures of the Media format Layer or in the Data Set encoding of an Information Object, the extension of such services in a manner that jeopardizes interoperability should not be done (e.g., File IDs longer than those specified in the DICOM File Service). The encapsulation of a DICOM File in a Secure DICOM File shall follow the specifications of Section 7.4 of this Part. These encapsulation rules define a mechanism for creating a Secure DICOM File by encapsulating an unprotected DICOM File as payload within a secure envelope DICOM Medical Information Directory In addition to the DICOM Image and Image related SOP Classes (e.g., results, patients) other SOP Classes tailored for media storage may be used to provide references (or directories) based on medical information, thus facilitating access to the clinical imaging information. Such a SOP Class is the Media Storage Directory SOP Class as defined in PS 3.4 of the DICOM Standard. Instances of this SOP Class are conveyed in the File with a File ID of DICOMDIR DICOM Media Storage Application Profiles A Media Storage Application Profile defines a selection of choices at the various layers of the DICOM Media Storage Model that are applicable to a specific need or context in which the media interchange is intended to be performed. Such choices are formally specified as a Media Storage Application Profile in order to ensure inter-operability between implementations conforming to the same Media Storage Application Profile. It facilitates conformance statements that allow users to assess interoperability of different implementations. Media Storage Application Profiles shall include: a. The description of the need addressed by the Application Profile (e.g., cardiac, echography, angiography) and its context of application; b. The selection, at the Data Format Layer, of a number of specific IODs and associated SOP Classes. For standard DICOM SOP Classes, this shall be done by reference to PS 3.4 of the DICOM Standard. These SOP Classes, like any other DICOM SOP Classes are assigned a unique registered UID. For each SOP Class it shall be stated if its support is required or optional within the context of this profile; c. The selection of a specific Media Format definition. This is done by reference to PS 3.12 of the DICOM Standard that specify the selected Physical Medium, a specific associated Media Format and the mapping of this Media Format (or file system) services onto the DICOM File Service; d. The selection of appropriate Transfer Syntaxes; e. The selection of a specific Security Profile. This is done by reference to PS 3.15 of the DICOM Standard which specifies the cryptographic algorithms to be used to encapsulate the DICOM Files of the DICOM File Set into Secure DICOM Files. If a Media Storage Application Profile selects no Security Profile, then the Application Profile is unsecure and the Secure DICOM File Format shall not be used with that Application Profile;
17 Page 17 f. Other choices facilitating interoperability such as specific limits ( e.g., maximum file sizes, if necessary, support of options, if any). The complete definition and structure of a Media Storage Application Profiles is specified by PS A number of Standard Application Profiles corresponding to different needs are included in PS Media Storage and the DICOM Standard Structure Figure provides an overview of the relationship between the functional areas identified by the DICOM Media Storage Model introduced in Section 6.2 and the various Parts of the DICOM Standard related to Media Storage. A number of Parts of the DICOM Standard are common between Network Communication and Media Interchange.
18 Page 18 General Network Communication Media Storage Interchange Part 2 Conformance Part 1 Overview Part 4 Service Class Specifications Part 3 Information Object Definitions Part 6 Data Dictionary (Images, Study, etc.) Part 11 Media Storage Application Profiles Part 5 Data Structure & Encoding Part 7 Part 10 Storage Media and File Format (Addressed by this Part of the Standard) Part 15 Security Profiles Part 8 Part 12 Media Formats and Physical Media Medium X Medium Y Medium Z Initial 9 Parts of DICOM Parts to support Media Storage Interchange. This Part of the DICOM Standard Figure Media Storage and DICOM Parts 7 DICOM File Format The DICOM File Format provides a means to encapsulate in a file the Data Set representing a SOP Instance related to a DICOM IOD. As shown in Figure 7-1, the byte stream of the Data Set is placed into the file after the DICOM File Meta Information. Each file contains a single SOP Instance.
19 Page 19 DICOM DICOM DICOM SOP Instance SOP Instance SOP Inst. DICOM Part 5 Encoding DICOM Part 5 Encoding DICOM File Meta Information DICOM Data Set DICOM File Meta Information DICOM Data Set A File contains one SOP Instance A File contains one SOP Instance More Files A File-set contains DICOM Formated Files 7.1 DICOM FILE META INFORMATION Figure 7-1 File-set and File Format The File Meta Information includes identifying information on the encapsulated Data Set. This header consists of a 128 byte File Preamble, followed by a 4 byte DICOM prefix, followed by the File Meta Elements shown in Table This header shall be present in every DICOM file. The File Preamble is available for use as defined by Application Profiles or specific implementations. This Part of the DICOM Standard does not require any structure for this fixed size Preamble. It is not required to be structured as a DICOM Data Element with a Tag and a Length. It is intended to facilitate access to the images and other data in the DICOM file by providing compatibility with a number of commonly used computer image file formats. Whether or not the File Preamble contains information, the DICOM File content shall conform to the requirements of this Part and the Data Set shall conform to the SOP Class specified in the File Meta Information. Notes: 1. If the File Preamble is not used by an Application Profile or a specific implementation, all 128 bytes shall be set to 00H. This is intended to facilitate the recognition that the Preamble is used when all 128 bytes are not set as specified above. 2. The File Preamble may for example contain information enabling a multi-media application to randomly access images stored in a DICOM Data Set. The same file can be accessed in two ways: by a multimedia application using the preamble and by a DICOM Application that ignores the preamble. The four byte DICOM Prefix shall contain the character string "DICM" encoded as uppercase characters of the ISO 8859 G0 Character Repertoire. This four byte prefix is not structured as a DICOM Data Element with a Tag and a Length. The Preamble and Prefix are followed by a set of DICOM Meta Elements with Tags and Lengths as defined in Table Table DICOM File Meta Information
20 Page 20 Attribute Name Tag Type Attribute Description File Preamble No Tag or Length Fields 1 A fixed 128 byte field available for Application Profile or implementation specified use. If not used by an Application Profile or a specific implementation all bytes shall be set to 00H. File-set Readers or Updaters shall not rely on the content of this Preamble to determine that this File is or is not a DICOM File. DICOM Prefix File Meta Information Group Length File Meta Information Version No Tag or Length Fields 1 Four bytes containing the character string "DICM". This Prefix is intended to be used to recognize that this File is or not a DICOM File. (0002,0000) 1 Number of bytes following this File Meta Element (end of the Value field) up to and including the last File Meta Element of the Group 2 File Meta Information (0002,0001) 1 This is a two byte field where each bit identifies a version of this File Meta Information header. In version 1 the first byte value is 00H and the second value byte value is 01H. Implementations reading Files with Meta Information where this attribute has bit 0 (lsb) of the second byte set to 1 may interpret the File Meta Information as specified in this version of PS All other bits shall not be checked. Note: A bit field where each bit identifies a version, allows explicit indication of the support of multiple previous versions. Future versions of the File Meta Information that can be read by verson 1 readers will have bit 0 of the second byte set to 1 Media Storage SOP Class UID Media Storage SOP Instance UID Transfer Syntax UID Implementation Class UID Implementation Version Name (0002,0002) 1 Uniquely identifies the SOP Class associated with the Data Set. SOP Class UIDs allowed for media storage are specified in PS 3.4 of the DICOM Standard - Media Storage Application Profiles. (0002,0003) 1 Uniquely identifies the SOP Instance associated with the Data Set placed in the file and following the File Meta Information. (0002,0010) 1 Uniquely identifies the Transfer Syntax used to encode the following Data Set. This Transfer Syntax does not apply to the File Meta Information. Note: It is recommended to use one of the DICOM Transfer Syntaxes supporting explicit Value Representation encoding to facilitate interpretation of File Meta Element Values. JPIP Referenced Pixel Data Transfer Syntaxes are not used. (See PS 3.5 of the DICOM Standard). (0002,0012) 1 Uniquely identifies the implementation that wrote this file and its content. It provides an unambiguous identification of the type of implementation that last wrote the file in the event of interchange problems. It follows the same policies as defined by PS 3.7 of the DICOM Standard (association negotiation). (0002,0013) 3 Identifies a version for an Implementation Class UID (0002,0012) using up to 16 characters of the repertoire identified in Section 8.5. It follows the same policies as defined by PS 3.7 of the DICOM Standard (association